已知函数f(x)=(sinx-cosx)sinx/sinx
1个回答

函数错了吧否则sinx直接与分母约去了

f(x)=(sinx-cosx)sin2x/sinx

=(sinx-cosx)*2sinxcosx/sinx

=(sinx-cosx)*2cosx

=2sinxcosx-2cos²x

=sin2x-(1+cos2x)

=sin2x-cos2x-1

=√2(√2/2*sin2x-√2/2*cos2x)-1

=√2(cosπ/4*sin2x-sinπ/4*cos2x)-1

=√2 sin(2x-π/4)-1(利用两角差的正弦公式得来的)